1. Statement of the Technical Field
The inventive arrangements relate to sensing algorithms for radio systems, and more particularly to systems for detecting occupancy of an RF frequency channel at low or negative signal to noise ratios.
2. Description of the Related Art
Cognitive radio systems are comprised of a network of radio transceivers that automatically change their transmission or reception parameters in response to a spectral environment. This process of dynamic frequency modification is sometimes referred to as dynamic spectral allocation (“DSA”). In such a system, the radio transceivers automatically choose the frequency on which to communicate with each other. The frequency used to communicate among network nodes is usually selected in such a way as to minimize interference with other users of the same spectrum. For example, the frequency can be selected to avoid interference with a class of wireless spectrum user which has been designated as a primary user of such spectrum. Alternatively, or in addition, the frequency can be selected to avoid interference with a source of interference, such as a jamming signal.
In a DSA system, the active control over the parameters of transmission and reception generally relies upon certain cognitive radio activities. These activities include spectrum monitoring and dynamic selection of transmission frequency among network nodes. To facilitate these processes, there is a need to determine occupancy of an RF frequency channel, e.g., by a primary user of the same spectrum or by any other interfering signal. Still, it can be difficult to quickly and efficiently determine channel occupancy when the signals involved have very low or negative signal to noise ratios. The problem is compounded in the military environment where nothing a priori is known about the primary user. In contrast, the primary user of a frequency spectrum is usually known in a commercial environment.
Current methods for detecting channel occupancy require a substantial amount of signal processing. Three common classes of detectors are known in the art for this purpose. The so-called Pseudo Spectrum method is the least sensitive and does a poor job of detecting wide-band signals. The Cyclostationary method is processing intensive and generally works best when a priori knowledge is available regarding the potential occupying signals. Finally, there is the so-called Eigenvalue method. This method is very sensitive and functions well for a wide range of signal types, but is very processing intensive and therefore not especially well suited for occupancy sensing which must be performed very quickly.